The rush to generate energy from wind and the sea is the main driver behind the Beauly to Denny line, according to Scottish and Southern Energy (SSE).
Scotland, like the rest of the UK, has been set targets for producing more power from renewable sources to help tackle climate change.
Sites in the north of Scotland will play major roles in doing that.
The Pentland Firth, Western and Northern isles have been identified as prime locations for "green" projects.
SSE said the transmission line between the Highlands and central Scotland must be upgraded to carry the volume of electricity created and to encourage greater competition in the market.
The existing line carries 132,000 volts (132kV), while the new one will be able to carry 400kV.
SSE said of the Beauly to Denny line: "The need for the country's green and more indigenous sources of energy is becoming increasingly acute and a rejection, or even partial rejection, of the replacement line will significantly delay Scotland's efforts to tackle climate change.
"Scotland's climate change commitments, industry confidence in renewables investment, broader economic development and employment in harnessing Scotland's renewable resources will all falter, at a time when the delivery of green energy solutions has never been more urgent."
The north of Scotland has been flagged up as key to the generation of renewable power.
First Minister Alex Salmond has previously described the Pentland Firth between Caithness and Orkney as the Saudi Arabia of marine power because of its tidal energy potential.
Developers have been invited by the Crown Estate, which owns the seabed, to pitch project ideas that would harness the firth's tidal energy.
The Crown Estate said the timetable for its leasing of the seabed and installation of renewable energy devices by 2020 remained on schedule.
It said legal paperwork opening the way for companies to harness wave and tidal power will be signed by the end of March.
Power could be generated for 500,000 homes by 2020, according to the organisation.
But the timetable was criticised by Thurso and Wick Trade Union Council which said the process was taking too long.
The council is eager to see new sources of work created to compensate for those that will be shed during the decommissioning of the defunct Dounreay nuclear power complex near Thurso.
Onshore wind projects are Scotland's biggest generators of renewable electricity, followed by hydro.
However, SSE said its flagship £140m Glendoe hydro electric scheme would not generate power at all this year.
Last August, a rock fall closed a tunnel carrying water from a hilltop reservoir to a massive turbine on the project near Loch Ness.
SSE said it was unlikely the plant would be running again until April 2011. A new tunnel may have to be built to bypass the damaged section.
When working, it can generate to a capacity of 100 MW - enough electricity for about 250,000 homes.
Meanwhile, SSE proposes to submit planning applications for two new hydro projects in 2011.
The pump storage schemes planned for Coire Glas at Loch Lochy and Balmacaan at Loch Ness would be the first of their kind in Britain since 1974.
The plants use two bodies of water located at different heights.
During periods of low demand for power, electricity is used to pump water from a lower loch to an upper reservoir and this water is then released to create power at a time when demand is high.